1. Field of the Invention
The present invention relates to a roots blower used with a supercharger of an engine for an automotive vehicle.
2. Description of the Prior Art
FIGS. 1 to 3 show an example of prior-art Roots blowers, in which the numeral 1 denotes a casing; 2 and 3 denote rotors rotatable within the casing 1; and 4 and 5 denote shafts rotatable together with the rotors 2 and 3, respectively. These two shafts are each supported by a pair of ball bearing units 6,7 and 8,9, respectively.
In these bearings, the bearing units 7 and 9 adjacent to timing gears 10 and 11, respectively are lubricated by a gear lubricant and leakage of the gear lubricant toward the rotor side can be prevented by two oil seals 12 and 13, respectively. On the other hand, the bearings 6 and 8 are lubricated by grease filling a ball bearing chamber C, and the grease is covered by two partitions 14 and 15 for prevention of grease leakage.
In the prior-art structure, however, because the grease within the chamber C leaks through gaps e.sub.1 and e.sub.2 during supercharge due to a difference in pressure between the chambers a.sub.1 and a.sub.2 and the chambers b.sub.1 and b.sub.2 caused by pressure fluctuations in the chambers a.sub.1 and a.sub.2 formed by the casing 1 and the rotors 2 and 3, there exist problems in that the bearings are not sufficiently lubricated due to lack of grease and therefore subjected to wear or seizure, thus shortening life of the bearings.